1. Field of the Invention
The invention pertains to the art of heat pumps (i.e., reversible refrigeration systems) and in particular to an arrangement for venting a higher pressure to a lower pressure following a reversal of the system.
2. Description of the Prior Art
One known problem experienced when heat pump systems are reversed, and in particular when the heat pump system has been operating in the heating mode and defrosting the outdoor coil is required, is that upon the shift to the defrosting cycle the suction line to the compressor is then connected to the high pressure interior of the indoor coil which had been functioning as a condenser, and the discharge line of the compressor is then connected to the low pressure interior of the outdoor coil which had been functioning as an evaporator. This momentary reversed pressure condition of a higher pressure at the suction side than at the discharge side of the compressor tends to result in expansion through it rather than compression. Since the compressor crankcase is open to the compressor suction line, the higher pressure tends to force crankcase oil up into the cylinders where it is pumped out into the system. To the degree that this oil pumping condition repeatedly occurs, the oil level may be reduced to a point causing a bearing failure in the compressor.
One known way to avoid this problem is to provide an arrangement in which the system is unloaded before the reversing valve changes to its final position. Such an arrangement also has as an object the reduction of the forces required to operate the reversing valve. Examples of arrangements of this general type are found in U.S. Pat. Nos. 2,597,729; 2,713,250; and 2,768,506. The first two noted patents have arrangements in which the reversing valve means operates only after the pressure differential within the system has completely or nearly disappeared, and use solenoid actuated unloader valves which may be tied into a time control circuit. The last noted patent provides an arrangement which includes a combination unloading and reversing valve and which is controlled in part at least by a common port on the valve connected to both the suction and discharge lines from the compressor through separate solenoid valve controlled lines. The combination valve includes a sequence, when a reversal is to take place, which includes leaking from the high pressure coil to the suction line to take away the valve shifting responsibility from one part of the device, and also includes substantially closing the suction line connection to, and opening the discharge line to, the low pressure coil. This results in drawing down the discharge line pressure. Subsequently, a valve element which has substantially isolated the high pressure coil from the discharge line is opened so that both the discharge line and the high pressure coil can feed high pressure refrigerant to both the low pressure coil and the suction line, this continuing until the coil pressures are equalized. Thereafter, through movement of several valve elements in response to changing pressure conditions, the system is set for the reversed operation. Thus the basic operation is that of unloading before the ultimate reversal is made, and in that sense the system is essentially the same as that of the other two patents and requires a delay as well as an unloading operation with refrigerant flow in both directions.
The aim of the present invention is to provide a substantially simpler arrangement and in which a simple, one direction check valve functions automatically after the reversing valve has operated to a reversed operation. The arrangement of the invention is considered preferable in that it is inexpensive, does not require complicated valve parts, and is not subject to the delay encountered when pressures are to be bled to equalize the system before the reversing valve changes position.